U.S. patent application number 10/916896 was filed with the patent office on 2005-03-31 for module for solid state relay for engine cooling fan control.
Invention is credited to Fissore, Sergio, Grant, William.
Application Number | 20050068735 10/916896 |
Document ID | / |
Family ID | 34381006 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050068735 |
Kind Code |
A1 |
Fissore, Sergio ; et
al. |
March 31, 2005 |
Module for solid state relay for engine cooling fan control
Abstract
A power module that includes a lead frame having conductive pads
molded in at the base thereof and a heatsink in thermal contact
with the conductive pads through a thermally conductive
adhesive.
Inventors: |
Fissore, Sergio; (Redondo
Beach, CA) ; Grant, William; (Fountain Valley,
CA) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Family ID: |
34381006 |
Appl. No.: |
10/916896 |
Filed: |
August 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60496000 |
Aug 14, 2003 |
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Current U.S.
Class: |
361/702 ;
257/E23.052; 257/E25.031 |
Current CPC
Class: |
H01L 2924/13091
20130101; H01L 25/165 20130101; H01L 2924/0002 20130101; H01L
23/047 20130101; H01L 2224/48137 20130101; H01L 23/49575 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
361/702 |
International
Class: |
H05K 007/20 |
Claims
What is claimed is:
1. A power module comprising: a lead frame, said lead frame
including a plurality of leads, and a plurality of spaced
conductive pads arranged in a common plane; a molded shell, said
molded shell including a plurality of molded walls defining a
space, and a base portion, said base portion including at least
said conductive pads said conductive pads being interconnected
mechanically and insulated electrically by mold compound disposed
between said spaced conductive pads; and a heatsink thermally
connected but electrically insulated from said conductive pads by a
thermally conductive adhesive.
2. A power module according to claim 1, wherein said leads include
at least two leads designated for connection to a motor extending
from said defined space through one of said walls; at least two
more leads designated for connection to a power source extending
from said defined space through another one of said walls, said
another one of said walls being opposite to said one of said walls;
and at least one lead designated for transmitting control signals
extending from within said defined space through said another one
of said walls.
3. A power module according to claim 2, wherein at least one of
said leads designated for connection to a motor and at least one of
said leads designated for connection to a power source are
integrated with at least one of said conductive pads.
4. A power module according to claim 3, further comprising a MOSFET
electrically connected at its drain side to said at least one
conductive pad.
5. A power module according to claim 4, further comprising a
free-wheeling diode having one pole thereof electrically connected
to another conductive pad, said another conductive pad being
integral with said other one of said leads designated for
connection to said motor; wherein said MOSFET is electrically
connected at its source side to another pole of said free-wheeling
diode.
6. A power module according to claim 5, further comprising another
MOSFET, said another MOSFET being electrically connected at its
drain side to a third conductive pad, said third conductive pad
being integral with another one of said leads designated for
connection to a power source.
7. A power module according to claim 6, wherein said another MOSFET
is electrically connected at its source side to said another
conductive pad.
8. A power module according to claim 7, further comprising a
circuit board disposed withing said defined space, said circuit
board including at least one gate driver for providing gate drive
signals to a gate electrode of each MOSFET.
9. A power module according to claim 1, further comprising a
thermistor disposed on one of said conductive pads.
10. A power module according to claim 1, further comprising a lid
attached to said walls, whereby said defined space is enclosed.
11. A power module according to claim 1, further comprising wires
electrically and mechanically attached to said leads and a soft
casing disposed over said leads and at least portions of said
wires.
12. A power module according to claim 1, wherein said soft casing
is formed from a soft polyamide.
13. A power module according to claim 1, wherein said adhesive is
loaded with thermally conductive particles.
14. A power module according to claim 13, wherein said thermally
conductive particles are comprised of alumina.
15. A power module according to claim 1, further comprising an
encapsulating body disposed within said defined space.
16. A power module according to claim 15, wherein said
encapsulating body is comprised of potting compound.
17. A power module according to claim 1, wherein said thermally
conductive adhesive is a thermally conductive adhesive tape.
18. A power module according to claim 1, wherein said molded shell
includes an integral mounting means adapted for mounting said
molded shell to a fan motor.
Description
RELATED APPLICATION
[0001] This application is based on and claims benefit of U.S.
Provisional Application No. 60/496,000, filed on Aug. 14, 2003,
entitled Module for Solid State Relay for Engine Cooling Fan
Control, to which a claim of priority is hereby made and the
disclosure of which is incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The power semiconductor devices of power systems are
typically integrated to form a power module. Most power modules
thus include power semiconductor devices, such as power diodes and
power MOSFETs. A power semiconductor device generate heat during
operation. The heat so generated affects the operation of the
semiconductor device, and also may have an adverse effect on the
structural integrity of the power module by for example creating
thermal stresses which may lead to fractures and other mechanical
damage. The heat generated by the power semiconductor devices must,
therefore, be extracted and dissipated. Otherwise the continued
operation of the power semiconductor devices may be
jeopardized.
[0003] In a conventional power module, the generated heat is
typically passed to a heatsink for dissipation. Serving as a
thermal conduit is usually a thermally conductive substrate which
is interposed between the heat generating power semiconductor
devices and the heatsink.
[0004] A known thermally conductive substrate is referred to as
insulated metal substrate (IMS). Another known thermally conductive
substrate is direct bonded copper (DBC). The use of an IMS or a DBC
is costly and increases the thermal resistance, which retards heat
extraction. Due to the less than ideal heat extractive capabilities
of a design that includes and IMS or a DBC, the reaching of the
maximum rating of a power semiconductor device is avoided to
prevent overheating, which may lead to inefficient power designs,
among other disadvantageous results.
[0005] Power modules are prevalently used in the automotive
industry, particularly for the driving and the control of electric
motors, among other uses. The increase in the number of features in
an average automobile has caused and continues to cause an
increased demand for generic or function-specific power modules.
Yet, the market place demands reduction of cost per module as well
as module efficiency so that the final cost of the car remains
competitive and electric power used by the extra features requires
as little extra power demand as possible on the automobile's
electric system.
[0006] Thus, it is desirable to have a power module which can
adequately dissipate the generated heat without using a thermally
conductive substrate.
SUMMARY OF THE INVENTION
[0007] A power module according to the present invention is adapted
to include the power elements of a high side driver for driving a
DC brushless motor. Specifically, the preferred embodiment of the
present invention is adapted for driving a DC brushless motor used
in an engine cooling fan structure.
[0008] A power module according to the present invention includes a
molded shell having a plurality of walls defining a space, and a
base portion. The molded shell further includes a lead frame having
a plurality of leads extending from the defined space through the
walls of the molded shell, and a plurality of conductive pads each
integrally connected with at least one lead. Each conductive pad
has at least one power semiconductor device electrically and
mechanically attached thereto by, for example, a layer of solder,
whereby the heat generated by the device is transferred to the
conductive pad. The heat so transferred is partially dissipated by
the leads integral with the conductive pad. The remainder of the
heat is transferred to a heatsink through a body of thermally
conductive adhesive, which attaches the heatsink to the conductive
pads. Thus, a module according to the present invention does not
require a thermally conductive substrate.
[0009] Mounting a semiconductor die such as a power MOSFET on a
conductive pad of a lead frame may also result in the lowering of
the overall resistance of the module in that the conductive pads
used may be thicker than those used when an IMS or a DBC is used.
Specifically, when an IMS or a DBC is used, the coefficient of
thermal expansion of the metal layer and the coefficient of thermal
expansion of the substrate require the thickness of the metal layer
to be kept below a certain minimum in order to prevent thermal
strains (usually resulting from thermal cycling) to cause the
conductive pad to peel off. Thus, for example, in a typical IMS the
conductive pads may be only 10-12 mils thick. Whereas, the
conductive pads in a module according to the present invention may
be made thicker, which results in reduced resistance and improved
heat dissipation.
[0010] A module according to the preferred embodiment of the
present invention includes other unique and advantageous features
which are described in detail in the following description and
shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0011] FIG. 1A shows a exploded view of a module according to the
present invention.
[0012] FIG. 1B a circuit schematic of a high side driver circuit as
incorporated in a module according to the present invention.
[0013] FIG. 2 shows a top plan view of a module according to the
present invention having the lid thereof removed for viewing its
internal elements.
[0014] FIG. 3 shows a bottom plan view of a module according to the
present invention having the heatsink thereof removed.
[0015] FIG. 4 is a first isometric view of a module according to
the first embodiment of the present invention.
[0016] FIG. 5 is a second isometric view of a module according to
the first embodiment of the present invention.
[0017] FIG. 6 is first isometric view of a module according to the
second embodiment of the present invention.
[0018] FIG. 7 is a second isometric view of a module according to
the second embodiment of the present invention.
[0019] FIG. 8 is a third isometric view of a module according to
the second embodiment of the present invention.
[0020] FIG. 9 illustrates a preferred use of a module according to
the present invention.
[0021] FIG. 10 is a circuit schematic of a high side driver which
is incorporated in a module according to the third embodiment of
the present invention. schematically illustrates the arrangement of
elements in a module according to the third embodiment.
[0022] FIG. 11 shows a top plan view of a module according to the
third embodiment without a lid to shows the internal components
thereof.
[0023] FIG. 12 shows a bottom plan view of a module according to
third embodiment having the heatsink thereof, and portion of the
shield thereof removed for illustration purposes.
[0024] FIG. 13 shows an isometric view of a module according to the
third embodiment.
[0025] FIG. 14 shows a top plan view of a module according to the
present invention.
[0026] FIG. 15 shows a bottom plan view of a module according to
the present invention.
[0027] FIG. 16 shows a side plan view along line 16-16 viewed in
the direction of the arrows shown in FIG. 14.
[0028] FIG. 17 shows a front plant view along line 17-17 viewed in
the direction of the arrows shown in FIG. 14.
DETAILED DESCRIPTION OF THE FIGURES
[0029] Referring to FIG. 1A, a power module according to the
present invention includes heatsink 1, thermally loaded adhesive
body 2, molded shell 3, solder layers 4, reverse battery MOSFET 7,
thermistor 6, high side driver MOSFET 5, free wheeling diode 8,
small diameter wirebonds 9, large diameter wirebonds 10, adhesive
layer 11, printed circuit board (PCB) assembly 12, encapsulating
body 13, and lid 14.
[0030] FIG. 1B shows a circuit schematic of a high side driver
circuit which is incorporated in a module according to the present
invention.
[0031] Referring now to FIGS. 2 and 3, molded shell 3, includes a
plurality of leads 20, 22, 24, 26, 28, 30, and a plurality of
conductive pads 32, 34, 36. Leads 20, 30 are unitarily integrated
with conductive pad 32 and extend through walls 40 of molded shell
40, lead 28 is unitarily integrated with conductive pad 34 and
extends through a wall 40 of molded shell 3, and lead 22 is
unitarily integrated with conductive pad 36 and extends through an
opposing wall 40 of molded shell 3. The phrase "unitarily
integrated" as used herein means that the lead and the conductive
pad are integrally connected to form a unitary body. To the
integral connection between the leads and the conductive pads a
portion of the heat generated by the semiconductor devices
(discussed below) disposed on the conductive pads is dissipated
through the leads.
[0032] As best seen in FIG. 3, conductive pads 32, 34, 36 are
spaced form one another. According to one aspect of the present
invention the spaces between conductive pads 32, 34, 36 are filled
with mold compound 38, which adheres to conductive pads 32, 34, 36.
Thus, mold compound 38 resides in the spaces between conductive
pads 32, 34, 36 and serves as electrical insulation as well as
mechanical support for laterally supporting conductive pads 32, 34,
36 in place.
[0033] Together, the combination of conductive pads 32, 34, 36 and
mold compound 38 constitute the base of molded shell 3 of a module
according to the present invention. Specifically, as best seen in
FIG. 2, molded shell 3 includes a plurality of walls 40 defining a
space and formed on base portion 42, base portion 42 including
spaced conductive pads 32, 34, 36 and mold compound 38. Preferably,
walls 40 are formed from the same material as mold compound 38 and
integrated with the same to form a unitary molded shell having
conductive pads 32, 34, 36 disposed at the bottom thereof.
[0034] As best seen in FIG. 3, conductive pads 32, 34, 36 are
exposed at the bottom of molded shell 3 at one side thereof, and
receive at least one semiconductor element at an opposing side
specifically. Specifically, high side driver MOSFET 5 is
electrically and mechanically attached to conductive pad 36 by a
layer of solder 4, free-wheeling diode 8 is electrically and
mechanically attached to conductive pad 34 by a layer of solder 4,
and reverse battery MOSFET 7 is electrically and mechanically
attached to conductive pad 32 by a layer of solder 4. In addition,
thermistor 6 is attached to conductive pad 32 by a layer of
solder.
[0035] As further seen in FIG. 2, a plurality of large diameter
bondwires 10 connect the source electrode of high side MOSFET 5 to
conductive pad 34, and a plurality of large diameter bondwires 10
connect the anode electrode of free-wheeling diode 8 to the source
electrode of reverse battery MOSFET 7.
[0036] PCB assembly 12 is disposed in the space defined by walls 40
and secured in place preferably by a layer of adhesive 11. PCB
assembly has disposed thereon a respective IC driver package 42 for
driving high side MOSFET 5 and reverse battery MOSFET 7. Each gate
driver package 42 receives drive signals from an external
controller through a respective lead 24, 26. Specifically, each
lead 24, 26 is electrically connected to a respective conductive
pad 44 by a respective small diameter bondwire 9, and each
conductive pad 44 may be electrically connected by any known manner
to a respective gate driver 42, whereby control signals from leads
24, 26 may be transmitted to respective drivers 42. Each gate
driver 42 is in turn, operatively connected to the gate electrode
of a respective MOSFET 5, 7. Specifically, small diameter bondwires
9 are used to connect a bondwire pad 46 to the gate electrode of a
respective MOSFET 5, 7. Each bondwire pad 46 is in turn
electrically connected by any known means (e.g. conductive traces)
to a respective gate driver 42, whereby drive signals may be
transmitted from a respective gate driver 42 to a respective MOSFET
5, 7. Thermistor 6 is also electrically connected to PCB assembly
12 in the same manner as the gate electrode of MOSFETs 5, 7 to
provide temperature information as is known in the art.
[0037] According to one aspect of the present invention, leads 20,
22 are power leads, leads 24, 26 are control leads, and leads 28,
30 are motor input and output leads. Thus, lead 22 is the power
input lead B.sup.+ from, for example, a battery, lead 20 is the
ground, lead 28 provides power to a motor and lead 30 is the
motor's ground connection. That is, a motor's ground connection (or
negative connection) is made through a lead provided in a module
according to the present invention.
[0038] To protect MOSFETs 5, 7, thermistor 6, free-wheeling diode
9, and PCB assembly 12, from moisture and the like encapsulating
body 13 is disposed inside the space defined by walls 40 of molded
shell 3. Furthermore, lid 14 is secured to walls 40 by an adhesive
layer 11 to enclose the space defined by walls 40. A potting
compound such as a silicone gel may be used for forming
encapsulating body 13.
[0039] Referring now to FIGS. 4 and 5, wires 48 are soldered to
leads 20, 22, 24, 26, 28, 30 and overmolded with a soft casing 50.
A preferred material for forming soft casing 50 may be a
soft-polyamide of the hot-melt variety which may overmold leads 20,
22, 24, 26, 28, 30 and at least the portion of wires 48 connected
thereto. Advantageously, soft casing 50 renders strength to leads
20, 22, 24, 26, 28, 30 as well as their connection to wires 48, and
protects the same from moisture and the like. Additionally, soft
casing 50 adds aesthetic qualities to the modules by providing a
"clean" exterior appearance.
[0040] Referring to FIG. 5, according to one aspect of the present
invention, heatsink 1 is thermally connected to base 42 of molded
shell 3. To facilitate the thermal connectivity of heatsink 1 to
base 42, and specifically to conductive pads 32, 34, 36, a
thermally loaded adhesive layer 2 is interposed between heatsink 1
and base 42. The use of a thermally loaded adhesive in combination
with heatsink 1 may eliminate the need for use of an expensive
element such as an insulated metal substrate (IMS) or double-bonded
copper (DBC), thereby reducing the cost of the module.
[0041] Thermally loaded adhesive layer 2 may be formed from any
known elastomer compound, such as a silicone, which has thermally
conductive particles such as Al.sub.20.sub.3 dispersed therein.
Preferably, the elastomer compound is selected to adhere heatsink 1
to base 42, aid in the transfer of heat from conductive pads 32,
34, 36 to heatsink 1, and electrically insulate heatsink 1 from
conductive pads 32, 34, 36. To further assist in mechanical
retention of heatsink 1 to molded lead frame 3, snaps 52 may be
provided on at least two opposing sides of molded shell 3. It
should be noted that snaps 52 are adapted to engage the body of
heatsink 1 in order to secure the same to molded shell 3.
[0042] Referring now to FIGS. 6, 7, and 8, a module according to
the second embodiment of the present invention does not include
soft casing 50. Rather, a module according to the second embodiment
of the present invention includes a shield 54 surrounding the
leads. Each shield portion 54 is preferably formed from the same
mold compound as that used for forming molded shell 3 and is
preferably integral with the same. Furthermore, preferably each
shield 54 includes a connector portion 56 which is adapted to mate
with a corresponding connector, e.g. a slot (not shown), on the
shell of an electrical connector (not shown) having electrical
connectors adapted for coupling with leads 20, 22, 24, 26, 28,
30.
[0043] A module according to the present invention is preferably
adapted for driving a brushless DC motor, such as fan motor used
for engine cooling. In one preferred embodiment, a power module
according to the present invention is a pass-through type module,
which will be connected directly to the fan motor, and fastened to
the fan shroud of the supplier of the fan assembly. To fasten a
module to a fan motor molded shell 3 includes a molded bracket 58
which is integral with a wall 40 of molded shell 3. Bracket 58
preferably extends from a wall 40 that is disposed between leads
20, 22, 24, 26, 28, 30. In addition, bracket 58 includes metal
mounting insert 60 which is adapted to receive a fastener such as a
screw to fasten molded shell 3 to a motor.
[0044] Thus, referring to FIG. 9, a power module 59 according to
the present invention can be mounted onto a motor 61 of a fan 62.
Due to the opposing orientation of leads 20, 22, 24, 26, and leads
28 and 30, power and control wires can be conveniently attached to
one side of module 59, while wires designated for connection to
motor 61 can be attached to the opposing side of module 59. Thus, a
module according to the present invention allows for the shortest
path for the wires, thereby reducing resistance and inductance
contributed by the wires. Furthermore, due to mounting on the fan
motor, a module 59 according to the present invention can be placed
in the path of the fan air flow. As a result, smaller heatsinks can
be used in a module 59 according to the present invention, thereby
reducing the size of module 60 and its cost.
[0045] A module according to the first embodiment and a module
according to the second embodiment are suitable for driving a
single fan motor. Thus, either embodiment may be connected in the
following manner: Battery(+) to Power Input, Power Output to Fan
Motor(+), Fan Motor (-) to Module, Module to Battery (-).
[0046] A module according to the present invention can be used to
drive two parallel connected fan motors. In this configuration, a
module according to the third embodiment is placed in series on the
positive bus. A module according to the third embodiment may be
connected in the following manner: Battery(+) to Module, Module
Output to Motor(+) (split into two outputs each going to a
respective fan motor), Motor (-) to Battery (Motor (-) from both
motors rejoin before connecting to the module). Thus, in a module
according to the third embodiment the battery connection in not
made through the module, but is made outside the module.
[0047] FIG. 10 is a circuit schematic of a high side driver
incorporated in a module according to the third embodiment of the
present invention.
[0048] Referring to FIG. 11, in a module according to the third
embodiment leads 22, 28, 20, 26 extend through only one wall of
molded shell 3. In addition, similar to the second embodiment, a
module according to the third embodiment includes shield 54
surrounding leads 22, 28, 20, 26. Furthermore, similar to the other
embodiments, a module according to the third embodiment includes
heatsink 1 which is in thermal communication with at least
conductive pads 32, 34, 36 through a thermally conductive adhesive
body 2 as seen in FIGS. 13-17. In a module according to the third
embodiment, IC driver package 42 for driving the high side FET 5 is
disposed on pad 36 alongside high side FET 3, and a driver circuit
for driving reverse battery FET 7 is formed on circuit board 12.
Circuit board 12 may be an IMS, DBC, an ordinary PCB or a thick
film. In all other respects, a module according to the third
embodiment is similar in construction to the first and second
embodiments.
[0049] Although the present invention has been described in
relation to particular embodiments thereof, many other variations
and modifications and other uses will become apparent to those
skilled in the art. It is preferred, therefore, that the present
invention be limited not by the specific disclosure herein, but
only by the appended claims.
* * * * *